In the manufacture of printed circuit boards from conventional photoresist elements, it is necessary to laminate the photosensitive layer of the element to the substrate board in such manner that the layer is firmly adhered thereto without occlusions and other phase discontinuities such as dirt or entrapped air. Furthermore, in many manufacturing situations, it is also desirable that a strong adhesive bond be formed instantly so that subsequent operations can proceed.
U.S. Pat. No. 3,547,730 discloses the lamination of photoresist layer to a substrate by passing the layer and substrate through the nip of heated spring-loaded laminating rolls. The photoresist layer and/or the substrate may be preheated prior to the lamination step. The purpose of this heating is to enable the layer to be forced into intimate contact with the substrate under the pressure of the rolls, whereby the layer achieves sufficient adhesion to the substrate to withstand subsequent photoresist processing steps such as solvent development and etching or plating of the substrate.
U.S. Pat. No. 3,629,036 discloses the use of a solution of photoresist to coat the substrate prior to lamination with a layer of photoresist. The coating solution purportedly enables sufficient adhesion to be obtained without heating being required for lamination. The coating solution is applied by pressing wicks against the substrate.
Though the prior art methods of lamination are satisfactory for many applications, there is a need for even more precise and uniform lamination methods, especially where printed circuit boards having a very high line density are being fabricated.